It is often important to establish and/or verify structural integrity of objects, components and structures. Loss of structural integrity in an object can be caused by material defects.
Non-Destructive Evaluation (NDE) methods refer to a class of methods that can be used to inspect objects for defects. NDE methods are often used to inspect materials for defects, such as structural anomalies, inclusions, cracks, etc. However, many conventional NDE methods often provide incomplete or otherwise inadequate inspections.
Recently, non-destructive evaluation methods commonly referred to as Thermal Acoustic Imaging (TAI) (or alternatively as acoustic thermography, sonic IR, thermosonic imaging, etc.) have been developed for detecting defects in objects in a fast and cost-effective manner. In general, TAI techniques use ultrasonic energy to excite an object being inspected, which causes the object and defective features therein to generate heat, which can then be detected using infrared (IR) imaging technologies.
In one exemplary TAI technique, an object that is being inspected is coupled to an ultrasonic broadband transducer. The ultrasonic broadband transducer is excited so that it couples a broadband acoustic signal into the object, which that introduces broadband sound energy into the object via acoustic waves. As acoustic waves are introduced into the object, the acoustic waves will cause defects in the object to vibrate.
To explain further, defects normally include opposing surfaces or interfaces, such as opposing edges of a crack, that move with respect to and against one another as the object is subjected to acoustic waves. Because the surfaces do not ordinarily vibrate in unison, they will rub against each other, which results in friction between or in the vicinity of the surfaces. Friction between the surfaces generates heat. Defects present in the object will heat up at a greater rate than other defect-free portions of the object, which are only minimally and uniformly heated. As temperature increases in the vicinity of the defect, infrared cameras or sensors can be used to detect defects that are discernable from other defect-free areas.
An infrared (IR) imaging device, such as thermal or infrared imaging camera, can then be used to capture images of the object that can be used to detect variations in temperature or infrared energy. For example, in some implementations, infrared energy can be detected using an IR camera that includes a two dimensional array of infrared detectors (pixels). Each pixel generates a signal that can be processed by an image processor to generate images. High resolution images can be captured by subtracting a background image (taken before acoustic excitation) from image(s) taken after excitation and recording the time derivative of the signal from each pixel instead the signal itself. Defects in the object will appear in the images as brighter areas in contrast to darker background areas that represent defect-free areas of the object.
Thus, thermal acoustic imaging techniques that combine acoustic induced heating with infrared imaging can be used as part of a very efficient, non-destructive defect detection system that can allow defects to be detected without needing to damage the object.
Although TAI techniques have proven successful for detecting defects in some objects in some environments, some presently available TAI techniques have drawbacks and limitations. For example, some presently available TAI systems can analyze only small areas (e.g., small objects or areas of objects), and are generally restricted to laboratory use. This can make it a difficult and time-consuming endeavor to inspect large objects or objects having a complex shape or geometry. Existing TAI techniques can often be complex to use when the object is particularly large and/or complex in shape and has many different areas or regions that require independent inspection.
In order for the TAI technique to work correctly, the IR imaging device must be positioned correctly and aimed at the correct location where defects might be located. If not, there is a risk that the imaging device will not detect the heat that is generated, and the defect may not be detected. This can happen for example, when the IR imaging device does not cover the entire surface of the object or is not aimed at the correct location of the defect. In addition, when a tight crack and a node are co-located (i.e., located in the same location), the IR imaging device may not be able to detect the presence of the crack since the object will not vibrate in that location.
It would be desirable to provide improved TAI methods, systems and apparatus for detecting defects, such as tight cracks, in an object being inspected. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.